An effective signal detection tool is necessary for a high-quality communication in the MIMO-system. Specifically, a V-BLAST detection scheme, as disclosed in P. W. Wolniansky, G. J. Foschini, G. D. Golden, and R. A. Valenzuela, “V-BLAST: an architecture for realizing very high data rates over the rich-scattering wireless channel,” in URSI International Symposium on Signals, Systems and Electronics, pp. 295-300, September), the contents of which hereby are incorporated by reference, employs the successive cancellation of the interference component, which does not require great computational resources and demonstrates good result when operating using rigid solutions at the output. However, this scheme includes a significant reduction in its effectiveness due to the maximum likelihood (ML) scheme that provides soft solutions, but is very strict to the computational resources.
One technical solution is described in the US Patent Application No. 2008/0152032A. This application proposes the method and apparatus that permit to use the signal detection based on the OSIC in the MIMO systems, the signal detection allowing for estimating the output bit probability, thus obtaining soft solutions.
The MIMO transmission system using m transmitting (Tx) antennas and n receiving (Rx) antennas is described Equation 1:y=Hx+v,  [Eqn. 1]
where H is the channel matrix of size n×m,
x=[x1 x2 . . . xm]T is the transmitted signal vector,
y=[y1 y2 . . . yn]T is the received signal vector,
v=[v1 v2 . . . vn]T is the noise component vector.
The classification procedure regulating the sequence for determining the transmitted symbols is based on the principle of the maximal norm of the channel coefficient matrix column, which permits primarily to choose the Tx antenna having the maximal value of the channel coefficient vector.
The detection method provides for estimating all possible transmitted signals layerwise, where the signal transmitted by one Tx antenna is regarded as the layer. Thus, such as in the case of the 16 QAM (quadrature amplitude modulation), sixteen (16) candidates are calculated first in the layer—1, which is determined as the best according the aforementioned classification procedure. Using the MMSE-OSIC method, symbols belonging to other layers are detected for every symbol from the layer—1, which results in forming sixteen (16) candidate vectors. K best candidates are separated amongst these sixteen (16) vectors, where K is a parameter which is set as K=3 for the example in the above application. The best candidates are determined in accordance with the minimum Euclidean distance criterion:d=∥y−Hxx∥2,  [Eqn. 2]
where xi is a candidate vector. Moreover, when calculating the Euclidean distance (2), the Logarithmic Likelihood Ratio (LLR) for the soft solution is determined:
                                          LLR            ⁡                          (                              b                i                            )                                =                                                    min                                  x                  ∈                                      S                                          i                      ,                      0                                                                                  ⁢                                                                                      y                    -                    Hk                                                                    2                                      -                                          min                                  x                  ∈                                      S                                          i                      ,                      1                                                                                  ⁢                                                                                      y                    -                    Hk                                                                    2                                                    ,                            [                  Eqn          .                                          ⁢          3                ]            
where i=1, . . . M; M is determined on the basis of the modulation type (M=4 in the case of the 16 QAM),
Si,0={x|bi=0} means symbols, for which the i-th bit is ‘0,’
Si,1={x|bi=1} means symbols, for which the i-th bit is ‘1.’
Thereafter, by means of scanning all possible symbols in the layer 2 when fixing K symbols from the layer—1, a next group of candidate vectors (consisting of K vectors) is determined. The solution vector for other layers is determined also using the MMSE-OSIC method. Thus, it is necessary to test m*K candidates. Values of the Logarithmic Likelihood Ratio (LLR) for the layer—2 are calculated by the Equation 3. Additionally, the LLR values for the layer—1 could be recalculated in the case, if a shorter Euclidean distance is obtained in comparison with the one calculated in the previous layer. Such procedure is similarly applied for all other layers. In order for processing every layer, the respective MMSE filter is determined:W1=(H1HH1+σ2I1)−1H1H,  [Eqn. 4A]
where H1=[h2 h3 hm] is the matrix H after exclusion of the column corresponding to the first layer,W2=(H2HH2+σ2I2)−1H2HH,  [Eqn. 4B]
where H2=[h3 . . . hm] is the matrix H after exclusion of the columns corresponding to the first and second layers.Wm-1=(Hm-1HHm-1+σ2Im-1)−1Hm-1H,  [Eqn. 4C]
where Hm-1=[hm] is the last column of the matrix H.
The disadvantage of the closest analogue consists in that, whereas the complexity degree of such a method is significantly lower than of the ML method, it is still nevertheless very high, especially in the case when the number of the Tx and Rx antennas is great.